Welcome to DTT.
As far as a good bike to start with, it depends on a few things.
1. How much can you afford?
2. How mechanically inclined are you?
3. What end result are you looking for? Full on custom cafe racer, or just a good solid bike with a few changes stylistically?
4. How will the bike be used? Short trips around town? Long weekend rides? Daily rider?
You definitly want a running bike, thats as complete as you can find to start. If you cant afford that, at least make sure its titled, doesnt have any major engine issues, and the expensive to replace bits are there (wheels, exhaust, carbs, etc...)
The Honda CB twin line (60's through the mid 70's) are terrific. The 160, 175, 200, 350, etc... All have a great aftermarket and are still affordable.
the XS650 is a badass bike. Aftermarket is as strong as the Hondas, and the amount of info out there in regards to customizing them is immense. They tend to be a bit more expensive though. Also, they are a taller bike, so for a short guy, who hasnt ridden on the street much, they can be a little tough to handle in stock trim.
There are lots of other great bikes out there though. Any of the Yamaha RD two strokes, or the Suzuki T250 and T500 are terrific bikes, though they are a little more rare so they'll cost more if you find one in good shape.
Another option, depending on you abilitly to fabricate and "build" parts is to go with something completely off the wall. There have been some really cool "cafe" interpretations built from vintage Harleys (big money), 70s and 80s era dirtbikes, etc...
Now, if money is no option, and you consider yourself a traditionalist of sorts, the Brit bikes are the way to go. Triumph, BSA, Norton, etc.
They will all cost a good deal more than any of the above bikes, as well as be more expensive when it comes to sourcing parts. They are some beautiful bikes though, and not to be dismissed. Hell, they were the cafe racers long before most of us were born.
Hope that helps. I just barely scratched the surface of whats possible. It all comes down to imagination, ability, and of course money.
Spend time doing research. Find finished racers that you really like. Search around this and other sites (but mostly this one
) and see what guys/gals are doing with their bikes.
Most importantly, dont bite off more that you can chew. Start small, with things youre comfortable doing to the bike and learn as you go. Nothing sucks more than staring at a dissasembled bike and thinking, "shit, what now?"
Good luck man! And if you find a bike, but are unsure whether its the right fit, just ask. We're here to help get ya on the road.